Large PA systems use a 70V audio bus to distribute power to speakers.
Each speaker has a transformer to drop the 70V down to the voltage
required for its own impedance and power level.  Often the amplifiers
are built to drive the 70V line directly.  But you can use a transformer
backwards driving a 20W 8ohm output winding to get 20W at 70V at the
input winding.  If you oversize the wattage you should be able to
stretch the 70V to 100V.

Have you considered using the transformer as a saturated core
oscillator?  The frequency and amplitude will drift a bit but it may be
good enough for lighting.

Sherpa Doug

> -----Original Message-----
> From: Timothy J. Massey [mailto:tmassey@MODERNMERCHANT.COM]
> Sent: Monday, April 15, 2002 10:46 AM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [EE]: 100VAC 10Khz 20Watts (or larger) - advice on
> build/buy ?
>
>
> Sent by:  Olin Lathrop <olin_piclist@EMBEDINC.COM>
>
> >> Unfortunately, even at 100w, an 8:1 transformer only gets
> >> you up to 28v.  You'd need 1250w @ 8 ohms to get to 100v
> with an 8:1
> >> transformer!
> >
> >Assuming a prefect transformer for now, an 8:1 transformer
> in this context
> >will step up the voltage by a factor of 8.  If 100V is desired at the
> >output, then 100/8 = 12.5V has to go into the transformer.
> Another way to
> >look at it is that the transformer changes volts and amps, but passes
> power
> >thru.  In other words, to get 20W out you need to put 20W
> in.  Since the
> >impedance has already been adjusted to appear as 8 ohms at
> the input, you
> >need an audio amp that can put out 20W into 8 ohms, which is readily
> >available.
>
> All correct.  My problem is that I was using the incorrect Ohm's Law
> formula I nit-picked about!  Stupid me:  I was figuring out
> how much power
> an amp would have to put out to generate 12.5_A_ @ 8 ohms,
> not 12.5v!  Yes,
> a 20w amplifier will work fine (ignoring efficency).
>
> >Of course a real transformer will dissipate some of the
> power, so you will
> >need to drive it with a bit more than 20W in.  If you can
> find one rated
> for
> >audio frequencies then it shouldn't be too bad.  A
> transformer intended
> for
> >60Hz power may not work very well at 10KHz.  You'll have to
> experiment.
>
> Yes, this is also a bit of an obstacle, but one that can be tackled by
> supplying more power.  You'll have to think about cooling the
> transformer:
> I don't know how hot it'll get.  It too, though, is an area that needs
> caution.
>
> Tim Massey
>
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